Group B Strep In Pregnancy

During the past two decades, group B streptococcus (GBS) has emerged as an important cause of newborn disease and death.  GBS is a kind of bacteria that is often found in the mouth or lower digestive, urinary or reproductive tracts in some men and women.  In women, it is most often found in the vagina and rectum.  It is different from group A streptococcus, which causes strep throat.

 GBS colonizes 15-40% of pregnant women at some time during their pregnancy.  A person who is colonized carries a bacteria but it causes no symptoms.  Being GBS colonized usually causes no illness for the mother, but it can be passed to the fetus.  It can also be passed to the baby after birth.

If GBS is passed from a woman to her baby, the baby may develop GBS infection.  Fortunately, almost all babies exposed to GBS (about 98%) do not become infected.  Babies who do become infected may develop early or late infections.

Early infections occur within the first seven days after birth.  Most occur within the first six hours.  Early infection can cause inflammation of the baby's lungs, blood, brain, or spinal cord.  Some of these babies become very ill and 15% may die.

 Late infections occur after the first seven days of life.  Only about 20% of GBS infections in newborns are late infections.  Late infections can cause serious problems, the most common of which is meningitis, inflammation of the brain or spinal cord.  Meningitis can have long-term effects on the baby's nervous system.  Babies with late infection are less likely to die.

Fortunately, there are tests to detect GBS.  Unfortunately, the tests are imperfect.  Cultures may be taken from the vagina and rectum late in pregnancy.  These cultures may take up to two days for results and may have false negative results.  Sometimes a woman can be not colonized when the sample is taken, but colonized later in pregnancy.  Thus, the test does not always detect women who will be positive for GBS at delivery.

Treating with antibiotics during labor is the best way to try and prevent GBS infection in the baby.  Treating the pregnant woman before labor is unreliable; if she is treated during pregnancy, the woman can become positive again after treatment.  If this occurs before her baby is born, she can pass GBS to her baby.

Risk factors for GBS also may help the doctor decide which women to treat.  Risk factors for GBS include pre-term labor, pre-term rupture of membranes, rupture of membranes more than 18 hours before the baby is born, having a prior baby with GBS infection, and fever during labor.

So, GBS is fairly common in pregnant women.  Yet very few babies actually become ill from GBS.  Risk factors and cultures help your doctor decide who needs GBS treatment in labor.  However, even appropriate GBS treatment in labor will not prevent all infections in newborn babies.

by Scott G. Williams, MD, FACOG, of SSM St. Charles Clinic Medical Group, O’Fallon, MO.